The overall goal of this application is to examine treatment modalities which may improve the clinical care of two groups of patients with congenital heart disease: infants born with a single ventricle supplying blood flow to the lungs and body and children with pulmonary hypertension associated with congenital heart disease. The primary hypothesis in infants with single ventricle is that chronic angiotensin converting enzyme (ACE) inhibition favorably modifies the ventricular remodeling response to volume overload and improves ventricular function over the first year of life. Serial changes in ventricular geometry will be assessed using magnetic resonance imaging and compared with measurements of systolic and diastolic function, including the pressure/volume relation and the Tei index, and clinical outcome measures including post-operative course and changes in the Ross? heart failure classification. The beneficial effect of ACE inhibition is expected to occur prior to and following volume unloading surgery with the bidirectional Glenn shunt or hemi-Fontan. The primary hypothesis of the study in congenital heart disease associated with pulmonary hypertension is that the effect of long-term treatment with an oral prostacyclin analogue or an oral endothelin receptor blocker has a salutory effect on exercise capacity, longevity, and quality of life. It will also be determined whether any of these patients carry a defect of the primary pulmonary hypertension-1 gene. Each of these studies could potentially lead to a significant improvement in prognosis: in the single ventricle group by preventing a long-term deterioration in ventricular function and in the pulmonary hypertension patients by improving quality of life and survival without transplantation.